Group 6
Rene A. Gajardo
Do Kim
Jorge L. Morales
Siddharth Padhi
Motivation
 Heavy course work would require more materials.
 Posture is affected by the larger amount of things that
a student carries.
 Knight Gear would allow for easier moving of school
materials and more.
Goals and Objectives
 Easy to use robot that follows the user using tracking
algorithm.
 Carry a limited load of materials for the user.
 Onboard ultrasound sensors
Specifications
Component
Design Specification
Chassis
1.5 in above ground
Length = 19.5in
Width = 15.5in
Height (max) = 21.75in
Height (min) – 12in
Ultrasound Detection
3m
Battery Life
2 hours
Battery Charge Rate
1.5 hours (electrically)
Wireless Connectivity Range
400 feet
Micro controllers
 One central microcontroller
 All the heavy computing
 Sensors
 Motors, and accessories.
 Does not need to be very powerful, but enough to be
able to handle and process all incoming data

Data is simplified by the smaller, weaker, outer
microcontrollers which handle the analog I/O from the
devices.
Micro Controller Comparison
MC68332
Intel 8051
PIC 18F452
Atmega
2560
Digital I/O
15
24
24
54
Analog I/O
15
8
8
16
Operating
Voltage
5V
3.3V
5.5V
3.3V
Cost
$11.94
$1.50
$4.68
$17.98
Why ATMega 2560 ?
 Popular option amongst hobbyist with a large




community for assistance
Programmable in C using Arduino
Enough memory for our needs
Allows Knight Gear to fully use all the Pulse Wave
Modulation lines that it required for all of the
ultrasound sensors and for the motor drivers.
With a 3.3 volt operating voltage, 54 digital I/O pins, 15
of them being PWM, 16 analog inputs, and a large
amount of documentation
 Pin
connections
of Mega Pro
3.3
Ultrasonic Proximity Sensor
 It engenders high frequency sound waves (above
20,000 Hz), which is incorporated in these sensors, to
measure the echo encountered by the detector, and is
then received after reflecting back from the target.
 This is the basic concept of how Knight Gear will detect
and follow its user.
Products Resolution
Reading Maximum
Rate
Range
Required Required Operational
Voltage
Current Temperature
Price
XLMaxSonar
-EZ
1cm
10Hz
300in-420in
3.5V-5.5V
3.4mA
0C – 65C
$27.95
XLMaxSonar
-AE
1 cm
10Hz
300in-420in
3.5V-5.5V
3.4mA
- 40C – 70C
$29.95
LVMaxSonar
-EZ
1 cm
20Hz
254in
2.5V-5.5V
2.0mA
-
$21.95
HRLV
MaxSonar
-EZ
1 mm
10Hz
195in
2.5V-5.5V
3.1mA
0C – 65C
$28.95
Parallax
PING)))
28015
1 cm
10Hz
118in
5V
30mA
0C – 70C
$29.99
Why PING))) 28015 ?
 Precise, non-contact distance
measurements. It is relatively
easy to connect to
microcontrollers
 PING))) 28015 measures
distance from about 2 cm (0.8
inches) to 3 meters (3.3 yards).
 Robot side only receive signals,
so cover the transmitter
 User side only send signals,
so cover the receiver
Sensors from
Maxbotix
Parallax Ping Sensor
Wireless Communication
 Wireless communication is needed for localization of
the user (which is the main feature of Knight Gear
and its top priority).
 Some wireless communications looked at were:
 Wi-Fi
 Bluetooth, and
 ZigBee
 ZigBee turns out to be the final choice for wireless
communication in Knight Gear.
Zigbee
 Low cost, low power, wireless mesh network.
 The following are the parameters of Zigbee
Parameters
ZigBee
Range
10-100 meters
Operating Frequency
2.4 GHz
Complexity
Low
Power Consumption
Low
Zigbee contd…
 Zigbee comes in 2 series. The following is the
comparison table between Series 1 and Series 2:
Parameters
XBee Series 1
XBee Series 2
Range
300 ft.
400 ft.
Power
Consumption
50mA @ 3.3v
40mA @ 3.3v
Frequency
2.4 GHz
2.4GHz
Data Rate
250 kps
250 kps
Cost
$22.95
$20.95
PNP Inverter
 We needed to invert a
serial signal from low to
high using a PNP
inverter.
 Using the serial out on
the XBee and inverting
it, we can get a high
pulse trigger for the
PING sensor
Solar Panel
 Increasingly popular
 No environmental pollution
 No need of burning fossil to generate the electricity
 Solar energy is no harm to our environment
 Generates electricity with no cost.
Solar Panel contd…
 The material of the panel was important due to the
different efficiencies of different materials in
transforming solar energy into electricity.
 There are several different types of solar panel in
used today. Some of the solar panels suitable for
Knight Gear were the following:



Monocrystalline
Polycrystalline
Amorphous
Solar Panel contd…
 Monocrystalline
 Most efficient (13-17%)
 These are one of the oldest and most sturdy ones
 Expensive, require extra time and energy
 Polycrystalline
 Efficiency (11-15%)
 One generally needs a larger polycrystalline solar panel
to match the power output of a monocrystalline solar
panel.
 Less expensive than monocrystalline
Solar Panel contd…
 Amorphous
 Non-crystalline silicon
 Amorphous solar panels are most found in calculators.
 The efficiency of amorphous photovoltaic cell is only
about 6-8%.
So, which one ?
 Polycrystalline solar panels
 To build our battery recharger for Knight Gear
 Even though this is less efficient than monocrystalline
panels
 It is very cost effective.
Wheels Configuration
 Mechanisms to provide locomotion that is required for
the Knight Gear
 Differential Drive
 Ackerman Drive
 Synchronous Drive, and
 Omnidirectional Drive
Differential Drive
 Wheels rotate at
different speeds when
turning around the
corners
 It controls the speed of
individual wheels to
provide directionality in
robot
 Correction Factor may be
needed to fix the excess
number of rotations
Chassis
 Custom made chassis designed out of High Density
Polyethylene (HDPE).
 Most chassis found where either too small or too big for
our needs.
 Withstands heat
 Water-resistant
Parameters
Measurements
Length
19.5 in
Width
15.5 in
Height (max)
21.75 in
Height (min)
12 in
Chassis contd…
Control Algorithm
 We implement a PI controller instead of a PID
controller to save memory.
 Runs only on current error and integral of previous
errors.
 Using small constant multipliers to lower the deviation
on Knight Gear.
 The error is determined by the time it takes for the
signal in the users transmitter to reach both sensors on
Knight Gear.
Control Algorithm Contd…
 The microcontroller pings the radio frequency antenna




on the user side transmitter
The user side transmitter then makes its Ping))) sensor
emit an ultrasound wave
The ultrasound sensors on the robot pick up on the
ultrasonic wave
The sensors return how far away the user is according
to each
The data is then sent to the PI Controller
 Class Diagram of
Knight Gear’s Control
Algorithm
Overall code
 The robot turns in the
direction of the of the
sensor which detected
the signal first.
 The magnitude of the
turn and the speed of the
robot is calculated by the
difference in time in
which the sensors detect
the user.
Motors
 Geared DC Motors
 Bigger, more powerful version of DC motor
 Used in robotics and other control situations where a
small motor with lots of power is needed.
 The speed is generally controlled using pulse width
modulation of the fixed input voltage.
 Can operate in both clockwise and counter clockwise
 Speed can be altered by varying the voltage applied to
the motor.
Motors cont…
Spur DC geared motors (x4)
 DC motor combined with a gearbox that work to decrease
the motor’s speed but increase the torque
 Pololu’s metal gear motor:
Operating voltage
6V
Free speed
120 RPM
Current
80mA @ free run
stall current
2A
Torque
9.6 lb*cm
Motor controller
 Microcontroller can decide the speed and direction of
the motor, but provide very limited and small output
current.
 Motor controller provides enough current and voltage
to the motor
 However, they cannot control how fast the motor should
spin. Therefore motor controller and microcontroller
need to work together to make the motors to move
properly.
Motor Controller
H Bridge
H bridge circuit is commonly used in robotics and other applications to
allow the DC motors to run forward and backward
0
1
1
0
Model
L293D
SN754410
DRV8833
Brand
Texas Instrument/
Stmicroelectrics
Texas Instrument
Texas Instrument
4.5V ~ 36V
4.5V ~ 36V
2.7V ~ 10.8V
1.2A
2A
1A
600mA
1.1A
500mA
H-Bridges
Quadruple-Half
Quadruple-Half
Dual
Control method
PWM
PWM
I2C / PWM
Internal diodes
YES
YES
YES
Price (from
mouser
electronic
website)
$1.12
$0.87
$2.58
Operating supply
voltages
Tolerant peak
output currents
Continuous
currents per each
channel
Why SN754410 motor controller ?
 Quadruple-Half h-bridge circuit -> control up to two
motors
 Provides sufficient continuous current of 1.1A
 Provides peak output current of 2A which is same as the
stall current of the motors
 No extra diodes are needed that makes easy to implement
the circuit
 Cost effective
Power source
Rechargeable battery selection
NiCad
NiMH
Alkaline
Li-ion
Voltage
1.25
1.25
1.50
3.6
Capacity load
Low
High
High
High
Recharge
Cycle
1000
500 - 1000
10 - 50
300 – 1000
Charging
Time
1 - 1.5 hours
2 -4 hours
2 – 3 hours
2 – 4 hours
Discharge
Efficiency
70 – 90 %
66 %
Varied by
Capacity Load
80 – 90
Operating
Temperature
-20 – 45 C
-20 – 45 C
-20 – 60 C
0 – 45 C
Self Discharge
Rate
10%
25%
<2%
8% at 20C
15% at 40C
30% at 60C
Why Nickel Metal Hydride ?
 High capacity
 Environmentally friendly
 NiMH batteries can be charged at any time without
affecting battery life
 Cost effective
Power System
 Motors draw too much of currents !
 Separate power source for motors (9.6V 2200 mAH)
 6V 2100 mAH battery pack is used for other electronic
devices
 Power Regulation required for other devices
 Power dissipation of other electronic devices
 (6V– 5V) * 330mA = 0.33W
 (5V-3.3V)*55mA = 0.094W
 Low dropout linear voltage regulators are used.
Linear Voltage Regulators
LM2940
LM3940
 LM2940 LDO regulator
 LM3940 LDO voltage
for 6V to 5V @ Io =1A
regulator for 5V to
3.3V@ Io =1A
Power system
power regulation cont.
 Block diagram of power system
9.6V
2200mAH
battery pack
6V 2100mAH
battery pack
Switch
6V -> 5V
LDO regulator
(LM2940)
Microcontr
oller
Motor
driver IC
Ultrasonic
sensors
5V -> 3.3V
LDO regulator
(LM3940)
Xbee RF
module
(wireless
antenna)
DC geared
Motors
Power system
power regulation cont.
 Block diagram of power system cont.
6V 2100 mAH
battery pack
Switch
6V ->5V
regulator
(LM2940)
5V -> 3.3V
regulator
Ultrasonic
sensor
Xbee RF
module
(LM3940)
Battery life test
 6V battery pack (robot side)  9.6V battery pack (robot side)
Part
Current draws
Part
Microcontroller
105 mA
4 x Gear motor @ 80 mA *4
free run
= 320 mA
Motor controller 115 mA
Ultrasonic
sensor (Rx)
50 mA
Xbee RF module 55 mA
(Tx)
Total
330 mA
 2100 mAH / 330 mA = 4.45 Hours




Current draws
4 x Gear motor
with
10 lb payload
340 mA *4
= 1360 mA
4 x Gear motor
with
20 lb payload
1090 mA *4
= 3360 mA
Free run -> 2200 mAH/320 mA = 4.81 hours
With 10 lb -> 2200 mAH/1360 mA =
1.13 hours
With 20 lb -> 2200 mAh/3360 mA =0.46hours
Xbee Testing
 This figure shows
how Xbee is
programmed to give
us the ID, high and
the low for the signal
which is shared by
the sender and
receiver.
Xbee Testing contd….
 This figure shows that
the Xbee is
communicating
successfully.
PI Controller Testing
 The values of the
ultrasound sensors are
printed in the com
 Components of the PI
controller are then printed
 Also the direction (left or
right) of the turn is printed
 Finally the adjusted speed
of the motors is printed
Technical Problems while building
Knight Gear
 Inconsistency in devices
 Ultrasonic sensors

Faulty and burned out sensors
 Weight sensor
 Xbee Antennas